Electrolytic cell system including upper and lower reacting chambers

ABSTRACT

An electrolytic cell assembly and system is provided which includes two or more modular units, each being provided for throughflow of electrolyte and includes a plurality of parallel alternately spaced anodes and cathodes, with the anodes and cathodes occupying less than the entire cross-sectional area of each unit. The end plates of each of the modular units are respectively an anode end plate and a cathode end plate. The electrodes project, preferably at right angles, from the end plates, but in staggered spaced-apart relation, so that each anode electrode (with the exception of the end ones) can be disposed between a pair of adjacent cathode electrodes and vice versa. The end plates are provided with either anode electrodes or cathode electrodes projecting, preferably at right angles, from one face. Between adjacent modular units are intermediate plates which, in one variant, are imperforate and act as combined anode and cathode holding and current transmitting plates. The intermediate plates are provided both with anode electrodes projecting from one face and cathode electrodes projecting from the other face. In another variant, the intermediate plates are porous to permit the throughflow of electrolyte and products of electrolysis from one modular unit to the neighboring one. The system includes means attached to each unit to bring cell products to a common upper reacting chamber, means connecting the upper reacting chamber to a common lower reacting chamber, and means connected between the lower reacting chamber and the units for introducing contents of the lower reacting chamber into each unit.

nited t1? esterinnd [75] Inventor: Gothe 0. Westerllund, Vancouver,

British Columbia, Canada [73] Assignee: Chenieclt Engineering Ltd,

Vancouver, British Columbia, Canada [22] Filed: June 28, 11971 [21]Appl. No.: 157,469

[30] Foreign Application Priority Data June 26, 1970 Canada 086626 [52]US. Cl 204M268, 204/95, 204/270, 204/275 [51] int. Cl non 3/00 [58]Field of Search 204/82, 95, 256, 204/258, 268, 270, 275

[56] References Cited UNITED STATES PATENTS 3,539,486 11/1970 Fleck204/95 1,485,461 3/1924 Knowles 204/256 2,944,957 7/1960 Keidel 204/2753,489,667 1/1970 Colman et al. 204/268 1,219,333 3/1917 Kynaston 204/275883,170 3/1908 Christy 204/268 FOREIGN PATENTS OR APPLICATIONS 791,6998/1968 Canada 204/95 Primary Examiner-John H. Mack Assistant Examiner-W.I. Solomon Att0rneyCushman, Darby & Cushman [111 Winfield [451 on, in,two

[5 7] ABSTRACT 'Ah electTolyticcell assembly andsysteniis provided whichincludes two or more modular units, each being provided for throughflowof electrolyte and includes a plurality of parallel alternately spacedanodes and cathodes, with the anodes and cathodes occupying less thanthe entire cross-sectional area of each unit. The end plates of each ofthe modular units are respectively an anode end plate and a cathode endplate. The electrodes project, preferably at right angles, from the endplates, but in staggered spaced-apart relation, so that each anodeelectrode (with the exception of the end ones) can be disposed between apair of adjacent cathode electrodes and vice versa. The end plates areprovided with either anode electrodes or cathode electrodes projecting,preferably at right angles, from one face. Between adjacent modularunits are intermediate plates which, in one variant, are imperforate andact as combined anode and cathode holding and current transmittingplates. The intermediate plates are provided both with anode electrodesprojecting from one face and cathode electrodes projecting from theother face. In another variant, the intermediate plates are porous topermit the throughflow of electrolyte and products of electrolysis fromone modular unit to the neighboring one. The system includes meansattached to each unit to bring cell products to a common upper reactingchamber, means connecting the upper reacting chamber to a common lowerreacting chamber, and means connected between the lower reacting chamberand the units for introducing contents of the lower reacting chamberinto each unit.

1 Claim, 7 Drawing lFigures Patented Oct. 16, 1973 W Swain-Sham 1.

1 R0 n mM/m MM YW s A W M 0 6 Patented Oct. 16,1973 3,766,044

4 Shwmtm-Shmt 2 INVENTOR GOT/V5 0. W55 rEeLu/VD L /ATTORNEYS PatentedOct. 16, 1973 3,766,044

4 Shoots-Shoot 4 INVENTOR 50 77/5 0. W25 7-591. .u/vp

ATTORNEYS ELECTROLYTTC CELL SYSTEM llNQlLlUlDllNG UlPflEllt AND LOWERlltlEACTliNG CHAMBERS BACKGROUND OF THE INVENTION This invention relatesto a modular electrolytic cell unit which is assembled as a multi-unitelectrolytic cell assembly to provide a compact system for highproduction. It also relates to the complete electrolysis system whichmay be provided therefrom.

Monopolar electrolytic cells provided with metal an odes and metalcathodes for the production of alakali metal chlorates from alkali metalchlorides are now extremely well known. However, plants employingmonopolar cells normally find it necessary to employ high amperage,about 20,000 to 150,000 amps, and low voltage which usually is expensivein capital cost for both power substation cost, bus bar cost and powerlosses by the current transmission losses. It is therefore manifest thatit is desirable to provide an electric cell and system in which thevoltage and amperage are optimized to provide high production foroptimum capital cost.

SUMMARY OF THE INVENTION a. Aims of the Invention An object of oneaspect of this invention is to provide a modular electrolytic cellassembly provided with metal electrodes in which the conventional busbar connections between cell units may be eliminated.

An object of another aspect of this invention is to provide such anassembly which offers high production output by the use of multiple suchmodular units.

An object of yet another aspect of this invention is the provision ofsuch modular units in the assembly which are electrically connected inseries so that the assembly will have a voltage equal to a unit voltagetimes number of such modular units.

An object of yet another aspect of this invention is the provision ofsuch a system which makes it practical to employ a rectifier powersubstation which is economically optimized by designing for a desirablevoltage: current ratio.

An object of yet another aspect of this invention is to provide suchmodular units assembled in such a way as to minimize the floor areacompared to conventional units of such throughput.

An object of still another aspect of this invention is to provide suchmodular units assembled in such a way as to minimize valving and pipingrequirements and to simplify control.

An object of a still further aspect of this invention is to provide suchmodular units assembled in such a way as to provide improved circulationof liquid due to gas lift and density differential.

b. Brief Description of Aspects of the Invention By the presentinvention, in its broad aspects, a modular electrolytic cell unit isprovided which includes two or more modular units, each being a doubleopenended, preferably cylindrical, chamber. in one variant of theinvention, each such chamber is provided with circumferential inlet andoutlet means for throughflow of electrolyte in a direction of flowparallel to, and between, adjacent, parallel alternately spaced anodesand cathodes. One end plate of the modular unit is an anode end plateand the opposite end plate is a cathode end plate. The anode end plateis disposed at, and seals, one open end, the anode end plate beingprovided with a plurality of spaced-apart anodes projecting from oneface thereof into the chamber. Similarly, the cathode end plate isdisposed at, and seals, the other open end, the cathode end plate beingprovided with a plurality of spaced-apart cathodes projecting from oneface thereof into the chamber in staggered alternate relationship to theanode electrodes which also project into the same chamber. In thisvariant of the invention, if two or more such modular units are providedin lateral, side-by-side relationship, each two adjacent such units areprovided with a common intermediate cathodeanode holding and currenttransmitting plate disposed at, and sealing, the adjacent open ends oftwo adjacent such cells. Such common plate is provided with a pluralityof spaced-apart cathodes projecting from one face thereof into the mainchamber in staggered alternate relationship to the anodes alsoprojecting into the main chamber, and a plurality of spaced-apart anodesprojecting from the other face thereof into the main chamber instaggered alternate relationship to the cathodes also projecting intothe main chamber.

In another variant of the invention, two or more such modular units areprovided in vertically stacked relationship. The lowermost of the unitsis provided with inlet means, e.g. circumferential inlet means for anintroduction of electrolyte. The uppermost of the units is provided withoutlet means, e.g. radial outlet means for the removal of electrolyteand both dissolved and gaseous products of electrolysis. One end plateof the modular units is an anode end plate and the other end plate is acathode and plate. The anode end plate is disposed at, and seals, oneopen end, the anode end plate being provided with a plurality ofspaced-apart anodes projecting from one face thereof into the chamber.Similarly, the cathode end plate is disposed at, and seals, the otheropen end, the cathode end plate being provided with a plurality ofspaced-apart cathodes projecting from one face thereof into the chamberin staggered alternate relationship to the anode electrodes which alsoproject into the same chamber. Each two adjacent such units are providedwith a common intermediate cathode-anode holding and currenttransmitting plate disposed at, and sealing, the adjacent open ends oftwo adjacent such cells. Such common plate is provided with a pluralityof spaced-apart cathodes projecting from one face thereof into the mainchamber in staggered alternate relationship to the anodes alsoprojecting into the main chamber, and a plurality of spaced-apart anodesprojecting from the other face thereof into the main chamber instaggered alternate relationship to the cathodes also projecting intothe main chamber. The sealing provided is between the cell units and theexterior of the cell units. The adjacent cell units are interconnectedby providing communicating apertures in the common holding plates. Thecurrent leakage is controlled by the cross-sectional area and length ofthe apertures.

By another aspect of each of these variants of this invention, the mainopen-ended chamber is cylindrical. Each open end is thus provided withan angular flange and each end plate is secured to the open end by meansengaging the angular flange, the means being clamped between a retainingring and the end plate being secured to the open end, a gasket beingdisposed between the open end and the end plate. When more than two suchunits are used, each intermediate plate is disposed between adjacentmodular units and simultaneously clamp the adjacent units together byspaced-apart means engaging the annular flanges, the means being clampedbetween a pair of spaced-apart retaining rings and the intermediateplate being secured to the open ends of the adjacent modular units, agasket being disposed between each open end and the intermediate plate.

The invention also provides in another of its variants, the provision ofany of the variants of electrolytic cell units described above incombination with a common upper reacting chamber, having liquor inletmeans from the cells, a brine inlet and gas outlet, and a lower reactingchamber having a liquor outlet means to the cell, and finished productoutlet. The cell assemblies direct effluent to the upper reactingchamber by gas lift and receive inlet from the lower reacting chamber.The two chambers are interconnected by a common connecting conduit,preferably through a heat exchanger. The reacting chambers are providedwith sufficient conduit piping to minimize current leakage.

Preferably, the combination includes a pair of such modular unitsystems, each cell in each system including: an effluent liquor riserpipe leading to an upper portion of the upper reacting chamber; a liquorinfeed riser leading from a lower portion of the lower reacting chamber;and including a common connecting conduit situated between the pair ofmodular unit systems, the conduit being provided with heat exchangermeans.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an idealized sideelevational view of a plurality of modular units of an aspect of thisinvention, assembled to provide a electrolytic cell assembly as ahorizontal unit;

FIG. 2 is an idealized central vertical section of the electrolytic cellassembly of FIG. 1;

FIG. 3 is a side elevational view, rotated through 90 of the anode andcathode plates of the embodiment shown in FIG. 2;

FIG. 4 is a section along the line IVIV of FIG. 3;

FIG. 5 is an idealized central longitudinal vertical sectional view of aplurality of modular units of another variant of this invention,assembled to provide an electrolytic cell assembly as a vertical tower;

FIG. 6 is an idealized side elevational view of a complete electrolysissystem embodying the electrolytic cell assembly of FIG. 1; and

FIG. 7 is an idealized cross-sectional view along the line VIIVII of theelectrolysis system of FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS a. Description of FIGS. 1 and 2Turning now to FIGS. 1 and 2, it is seen that the multi-unitelectrolytic cell system 10 includes a plurality, in this case 4,modular cell units 11. Structurally, each modular cell unit includes acylindrical tube 12, open at each end 13, 14 and provided with alignedcircumferential liquor inlet cylindrical nozzle 15 and liquor effluentcylindrical nozzle 16. The circumferential lip adjacent opening 13 isprovided with an angular and annular flange 17, while thecircumferential lip adjacent opening 14 is provided with an angular andannular flange 18. An end plate 19, in this case a cathode end plate, issecured to the tube 12 at open end 13 by means of annular retainingflange 20, which has an angular surface mating angular surface of flange17, and retaining ring 21, all being held together with suitabletension, and with liquor-tight and electrically nonconductive gasket 22disposed at the open end 13, by means of bolt and nut combinations 23,passing through aligned apertures in retaining ring 21 and cathode endplate 19 respectively. An anode end plate is of the same structure ascathode end plate 19 and may be secured at open end 13 in a similarmanner.

A combined cathode-anode intermediate plate 24 is provided betweenadjacent modular units 11, and the means holding the plate 24 to theadjacent units 11 also holds adjacent units 11 together. Thus, gasket 25is placed at open end 14, an annular retaining flange 26 is placed inmating relation to flange 18, and retaining ring 27 is placed againstannular retaining flange 26. Gasket 22, annular retaining flange 21, andretaining ring 23 are placed at open end 13 of the adjacent tube 12 ofmodular unit 11. Then the sub-assembly is assembled by means of nut andbolt combinations 28 passing through aligned apertures in retainingrings 23, 27 and intermediate plate 24.

The main body or tube 12 of the modular electrolytic cell 11 ispreferably formed of glass for several reasons, namely, that it is (i)chemically resistant: (ii) transparem; and (iii) electrically resistant.One alternative to using glass tube 12 is to use steel, but in thiscase, the tube 12 should be electrically connected to the cathodes forprotection against corrosion. It is, of course, absolutely essentialthat tube 12 be electrically isolated from the anodes, e.g. by gasketsand spacers. Another alternative is to make the tubes of titanium, whichis chemically resistant to the liquor and does not require cathodicprotection. To avoid the need for cathodic protection, the voltagepotential is controlled to under 6 volts for current flow from thecontainer. As shown, it is preferred to have a multi-unit assembly 10comprising many units, e.g., one plant is designed for l2 units in oneassembly.

b. Description of FIGS. 2, 3 and 4 Turning now to FIGS. 2, 3 and 4, itis seen that the intermediate plate is provided with a plurality ofanode plates 29 on one face 30 thereof and a plurality of cathode plates31 on the opposite face 32 thereof. Plate 24 may be a composite plate,e.g. one side steel to provide face 32 for the cathode electrodes 31,the other side titanium with noble metal of the platinum group or itsoxides coating to provide face 30 for the anode electrodes 29. Suchcomposite plates are commercially available, e.g. from Du Pont, underthe Trade Mark DETACLAD.

The electrodes may be welded to the holding plate or connected. Asclearly seen in FIG. 2, the anode and cathode electrodes 29, 31respectively are offset to fit precisely in between each other whenassembled to an adjacent unit. The interelectrode space varies between 2and 10 mm. The end plates 19 are, of course, either an anode or acathode, but would have the same construction features as theintermediate electrode assembly.

c. Description of FIG. 5

Another variant of the invention is shown schematically in FIG. 5. Themulti-unit electrolytic cell system is a vertical tower of plurality, inthis case nine, cells or compartments 111. The number of suchcompartments may, however, be as few as two, or as many as 50. Eachshell of the cell or compartment 111 is a cylindrical tube 112 formed,for example, of plastics material, e.g. polyvinyl chloride, polystyrene,etc. or glass.

Structurally, then, each modular cell unit or compartment 111 includes acylindrical tube 112, open at each end 113, 1141. The circumferentiallip adjacent opening 113 is provided with an angular and annular flange117, while the circumferential lip adjacent opening 1141 is providedwith an angular and annular flange 113. An end plate 119), in this casea cathode end plate, is secured to the tube 112 at open end 113 by meansof annular retaining flange 120, which has an angular surface matingangular surface of flange 117, and retaining ring 121, all being heldtogether with suitable tension, and with liquor-tight and electricallynonconductive gasket 122 disposed at the open end 1113, by means of boltand nut combinations 123, passing through aligned apertures in retainingring 121 and cathode end plate 119 respectively. The anode end plate11111 is similar in structure to the cathode end plate 191 and may besecured to open end 113 in a similar fashion.

A combined cathode-anode intermediate plate 1241 is provided betweenadjacent modular units 111, and the means holding the plate 1241 to theadjacent units 111 also holds adjacent units 1111 together. Thus, gasket125 is placed at open end 114, an annular retaining flange 126 is placedin mating relation to flange 113, and retaining ring 127 is placedagainst annular retaining flange 12b. Gasket 122, annular retainingflange 121, and retaining ring 123 are placed at open end 113 of theadjacent tube 112 of modular unit 111. Then the sub-assembly isassembled by means of nut and bolt combinations 12% passing throughaligned apertures in retaining rings 123, 127 and intermediate plate124.

As described hereinbefore with reference to FIGS. 1 41, the main body ortube 112 of the modular electrolytic cell 111 is preferably formed ofglass for several reasons, namely, that it is (i) chemically resistant;(ii) transparent; and (iii) electrically resistant. One alternative tousing glass tube 11112 is to use steel, but in this case, the tube 112should be electrically connected to the cathodes for protection againstcorrosion. It is, of course, absolutely essential that tube 112 beelectrically isolated from the anodes, e.g. by gaskets and spacers.Another alternative is to make the tubes of titanium, which ischemically resistant to the liquor and does not require cathodicprotection. To avoid the need for cathodic protection, the voltagepotential is controlled to under 6 volts for current flow from thecontainer. As shown, it is preferred to have a multi-unit assembly 110comprising many units, e.g., one plant is designed for 12 units in oneassembly.

The intermediate plate 12 1 is provided with a plurality of anode plates129 on one face thereof and a plurality of cathode plates 131 on theopposite face thereof. Plate 121 may be a composite plate, e.g. one sidesteel to provide the face forthe cathode electrodes 131, the other sidetitanium with noble metal of the platinum group or its oxides coating toprovide the face for the anode electrodes 129. Such composite plates arecommercially available, e.g. from Du Pont, under the Trade MarkDlETACLAD.

The electrodes may be welded to the holding plate or connected. Theanode and cathode electrodes 129, 131 respectively are offset to fitprecisely in between each other when assembled to an adjacent unit. Theinterelectrode space 11341 varies between 2 and mm. The

end plates 1119 are, of course, either an anode or a cathode, but wouldhave the same construction features as the intermediate electrodeassembly.

It is seen that the lowermost unit of the plurality of stacked units 111includes a circumferential liquor inlet nozzle 11S, and the uppermostunit of plurality of stacked units 111 includes an axial product outlet116, carrying liquor and evolved gas which is entrained and- /oroccluded within the liquor.

It is also seen that the holding plates 12 1- are provided withperforations 131} thereby to channel the reactant liquor and theproducts of the reaction from the bottommost unit to the uppermost unit.The arrows 132 show the flow of the reactant liquor and the productthrough the plate 1241 or an insert in the plate 124.

It will be observed that there is a non-electrolytic space 133. Assumingthe electrodes 129, 130 do not seal tightly to the container 112, i.e.communicate with side sections and that there is a significant pressuredrop for flow through the openings 1311 in the holding plate 1241, therewill be a significant internal circulation between the side sections ornon-electrolytic spaces 133 and the space 1341 between electrodes.

It is seen that the assembly in FIG. 5 is basically the same as theassembly of FIGS. 11 and 2 earlier described. However, it will be notedthat the flow through the assembly is longitudinally therethrough.Preferably all of the liquor to the assembly is fed to the lowest unitin the assembly through inlet nozzle and liquor and gas are channelledfrom one unit to the other, preferably by openings 1311 in the electrodeholding plates 12 1 and finally discharged to a reactor from the topunit through outlet nozzle 1116. The current leakage is controlled bycross-sectional area of the openings 1311 in the plate 1241 and thethickness of electrode holding plate 124. While not shown, the apertures1311 may be provided with hollow cylindrical inserts for annealing theeffluent liquor and product gases. Then, the current leakage would begoverned by the cross-sectional area of the hollow cylindrical insertsand the length of such inserts.

The main advantages of such vertical assembly compared to the horizontalassembly include the following, namely: (1) the floor area requirementis drastically reduced; (2) one inlet for the liquor and one outlet forthe product for each assembly is possible, thus minimizing valving andpiping requirements and simplifying control; and (3) the assembly worksessentially as a column containing a product of significantly lowerdensity then the liquor feed; thus, the gas lift as well as the densitydifferential cooperate in improving the circulation of liquor throughthe assembly.

It is also noted that the electrodes 129, 131 do not normally cover theentire cross-sectional area of the cell container. Thus, the designincorporates internal circulation. This is an especially importantfeature of the design when the assembly is erected vertically, since theinternal liquor circulation resulting from the gas evolution on theelectrode surface provides for interchange of electrolyte between theelectrodes and standardizes conditions in the cell chambers.

While not shown in detail, the vertical assembly design may be designedto make the column size sufficiently large to provide mainly by means ofnonelectrolytic spaces 133 in the compartment the total desirableelectrolyte volume and retention time for chemical reactions tochlorate. In this case, no external recirculation would be required.This is very desirable in some aspects since it minimizes pipingrequirements and provides cascade arrangement between compartments, orcells, under favourable conditions. Thus, electrolyte (brine) enters atthe lowest compartment and finished product leaves at the topcompartment, the retention time being provided in each and everycompartment. This construction provides the conditions for conversion ofhypochlorite to chlorate in each compartment. Temperature control couldbe maintained by, for example, installing a cooling coil in hecompartments or jacketing the columns. On the other hand, with thevariant of FIGS. 1 and 2, a separate cell assembly may be installedindoors and the reactors outdoors.

The electrode assembly may be fitted inside a larbe tube (e.g. a glasscolumn) rather than dividing the column into sections. The electrodeholding plates would then be placed between sections.

While the assembly has been shown vertical, it may be inclined tovarious degrees up to and including vertical installation, i.e., from Oto 90 relative to the horizontal.

d. Description of FIGS. 6 and 7 Turning now to FIGS. 6 and 7, it is seenthat a pair of multimonopolar electrolytic cell assembly and system 10is disposed between and interconnected to an upper reaction chamber 36and a lower reaction chamber 37 to provide an electrolysis system 35.Each outlet nozzle is connected to an effluent riser pipe 38, each riserpipe extending upwardly within upper reaction chamber 36 to terminatenear the top thereof at outlet 39. Entrained and/or occluded gasesformed during the electrolysis reaction are permitted to separate fromthe liquor 40 and to pass upwardly into a gas chamber 41 provided with afrangible cover 42 (for safety reasons) and with a gas outlet nozzle 43leading away from the electrolysis system. Fresh brine is introducedthrough cylindrical inlet nozzle 44 which extends downwardly into theupper reaction chamber 36 to terminate in a submerged outlet 45.

Degassed liquor in which the reaction to chlorate has been at leastpartially completed passes through a common connecting conduit 46disposed between the pair of multi-unit cell systems 10 and passesthrough an annular heat exchanger 47 having cooling water inlet 48 andwater effluent 49. If desired, the heat exchanger may be cooling coilsdisposed in the lower reaction chamber 37, or any other suitable means.From the lower reacting chamber, an inlet riser pipe 50, connected toeach inlet nozzle 15 of cell 11 originates at an inlet 51 near thebottom of chamber 37 and brings liquor 53 from lower reacting chamber 37to cells 11. Finished product chlorate is withdrawn from outlet nozzle54 at the bottom of chamber 37 and passes via outflow conduit 55 leadingto chlorate storage (not shown).

During the course of the electrolysis, gases produced are in the liquorin the form of entrained or occluded bubbles. This reduces the densityof the liquor to such an extent that the effluent liquor is pumped, bygas lift, up effluent riser pipes 38 and is sucked upwardly throughinlet riser pipes 50. The pipe risers 38 and 50 provide sufficientpiping to minimize current leakage.

In the example where the cells 11 are used for chlorate electrolysis,the electrolyte is brine and the electrolytic products are:hypochlorite, chlorate and hydrogen gas, as well as by-product oxygenand water vapor.

Since the electrolysis is of sodium chloride brine with no diaphragm,the effluent, consisting of C1 Na, H OH, ClOH, Cl, H", and OCl' and inthe form both of liquor and gaseous products, pass from effluent piperisers 38 to upper reacting chamber 36. The level of the liquor 40 inupper reacting chamber 36 is shown by level line 52 and is higher thanoutlets 39 so that liquor and gaseous products are separated from oneanother. The upper portion of the upper reacting chamber 36 consequentlyacts as a degasifier. Recycle liquor passes down through upper reactingchamber 36 through common conduit 46 to lower reacting chamber 37.

The liquor velocity through upper reacting chamber 36 is reduced to suchan extent that optimum separation of the entrained gases takes placewithout shortcircuiting through the tank, which would result from toolow a liquor velocity. The velocity, on the other hand, must besufficient to utilize the entire vessel but not too rapid to inhibit theexpulsion of any further entrained and/or occluded product gases. Theoptimum velocity is a function of the apparent density of the liquid,which, in turn, is dependent on the amount of entrained gases and thebubble size. It has been found that a liquor velocity of about 10ft/min. can separate substantially 100 percent of the entrapped gases.

Upper reacting chamber 36 and lower reacting chamber 37 combined are forthe purpose of permitting the reaction to take place. For any selectedtemperature, the retention time in reacting chambers 36, 37 is afunction of the concentration of ClOH and C10" present in the liquorwhich in turn is directly related to the current density. Thus, it wasfound that to yield a current efficiency of greater than percent, with aconstant recirculation of liquor and a pH ofrapproximately 6.5, thecurrent concentration should be less than 7 amps/ litre at 80C. or lessthan 6 amps/litre at 60C. The current concentration (in amps/litre) isthe main determining factor in calculating the reacting chamber volume.The retention time, on the other hand, is dependent on the rate of theliquor circulation, as well as on the volume of the reaction vessel.

The liquor entering the upper reacting chamber 36 may have temperaturesranging from about 45 to C., preferably between about 60 and 80C. FIGS.6 and 7 show a heat exchanger 47 which is provided for temperaturecontrol. The reacting chamber parameters are such that there is asufficiently long retention time of liquor in reacting chambers 36, 37to favour the desirable reaction NaOCl 2l-lClO NaClO +2116].

It is also important to minimize the concentration of the hypochloritefor if his too high, it will decompose and anode electrode coating wearincreases. In addition, the pH should be maintained below 7.5 andpreferably between about 5 and 7. At a pH of 6.8, the optimum reactionof 2 moles of HClO to 1 mole of NaOCl takes place if no dichromate ispresent.

Effluent from the lower reacting chamber 37 is conveyed to cells 11through inlet pipe riser 50 to inlet nozzle 14. Gas is drawn off atoutlet 43 from gas chamber 41. Gases, consisting of H2, H O (vzfpor), OCOQaiid Cig may be vented as waste through outlet 43 or may be utilized.

H Cl 2ll-[Cl (producing hydrogen chloride) 2H ZH O (producing watervapor) The hydrogen chloride may be recovered as hydrochloric acid byscrubbing with water.

It is generally known that the oxygen content of the cell gas decreaseswith a lower pH of the electrolyte simultaneously as the chlorine lossesincrease. Using a combustion chamber for the recovery of chlorine lossesas hydrochloric acid, the cell may be operated at a low pH and thusbenefit by the resulting improved current efficiency.

Thus, it should be pointed out that the cell apparatus may be usedemploying forced circulation. The process system hereinabove discussedutilizes the gaseous products as a means to create a lift in theexternal pipe riser and thus does not require any means for forcedcirculation.

In the above-described assembly containing the cells llll, gasesproduced in the cell assemblies llll rise in the pipe riser and thuscause recirculation of liquor. Two reactors are preferred, but the cellassemblies may also be used with a system employing one reactor only. Anexternal heat exchanger is desirable for easy maintenance and to achievea high U-value by the higher velocity compared to a heat exchanger (orcoil) which may be placed inside the upper reacting chamber 36.

Current flow is from one end of the cell assembly through first unitanode electrodes 1W via the cell electrolyte space to the cathodeelectrodes of the intermediate holding plate 24.1 and then into thesecond unit and so on until the current leaves at the opposite end ofthe electrode assembly.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Consequently, such changes and modifications are properly,equitably and intended" to be, within the full range of equivalence ofthe following claims.

I claim:

ll. An electrolysis assembly comprising in combination: A) a pair ofmulti-unit cell systems, each comprised of at least two units disposedhorizontally in lateral end-to-end relationship, each such unitcomprismg:

a. an open-ended main chamber including inlet ilfll means for the flowof electrolyte to, and between adjacent, parallel, alternately spacedanodes and cathodes and outlet means constructed and arranged towithdraw electrolyte along with gaseous products of electrolysisentrained and/or occluded therein from the chamber, said chamber beingelectrically isolated from said anodes and cathodes;

b. an anode end plate disposed at, and sealing one open end of saidchamber, the anode end plate being provided with a plurality ofspaced-apart anodes projecting from one face thereof into said chamber;

c. a cathode end plate disposed at, and sealing the other open end ofsaid chamber, the cathode end plate being provided with a plurality ofspacedapart cathodes projecting from one face thereof into said mainchamber in staggered alternate relationship to the anodes alsoprojecting into said chamber;

said anodes and cathodes occupying less than the entire cross-sectionalarea of the chamber thereby to provide at least one non-electrolysiszone within said unit, thereby to enable internal liquor circulationresulting from gases evolved on the electrode surfaces to interchangeelectrolyte between the electrodes and to provide substantiallyhomogeneous conditions in the chamber; the plate between two adjacentsuch units being a common intermediate cathode-anode holding and currenttransmitting plate disposed at, and sealing the adjacent open ends ofsaid two adjacent such units, and being provided with a plurality ofspaced-apart cathodes projecting from one face thereof into one suchunit in staggered alternate relationship to the anodes also projectinginto said unit from the other end thereof and a plurality ofspaced-apart anodes projecting from the other face thereof into theother such unit in staggered alternate relationship to the cathodes alsoprojecting into said unit from the other end thereof;

B. a common upper reacting chamber having a liquor inlet connected tosaid cell system, a brine inlet and a gas outlet;

C. a common lower reacting chamber having a liquor inlet, a liquoroutlet connected to said cell systems to feed said systems and afinished product outlet; and g D. a common conduit interconnecting theupper reacting chamber and the lower reacting chamber, said conduitbeing located between the pair of cell systems and being provided withheat exchanger means;

the circulation between cell systems, upper reacting chamber and lowerreacting chamber being by means of gas lift, each unit in the cellsystems including an effluent liquor riser pipe leading to a portion ofthe upper reacting chamber and a liquor infeed riser leading from alower portion of the lower reacting chamber.

:1: :i: :{x it: fllt

